1. Field of Invention
This disclosure pertains to towing aids for flat-towed vehicles. More particularly, this disclosure pertains to carriers that are placed under the front wheels of a flat-towed vehicle when the towing and towed vehicle are being maneuvered together in reverse.
2. Description of the Related Art
In the field of powered recreational vehicles (“RVs”), it is common to tow a small second vehicle for local transportation when a destination is reached and the RV is parked and connected to services. The towed vehicle is sometimes referred to as a “toad,” or more commonly as a “dinghy.”
The most common method of towing a dinghy is referred to as “four-down” or “flat-towing,” where all the wheels of the dinghy remain on the road during towing. The advantages of flat-towing include a quick, easy connection and disconnection of the dinghy from the RV; no additional vehicles such as a flatbed trailer or tow dolly needing to be stored when the dinghy is not being towed; and the special tow bar required for flat-towing remaining attached to one of the vehicles and simply folded and locked when not in use.
However, there is one significant disadvantage to flat-towing: the RV and dinghy cannot be moved in reverse when they are connected, i.e., they cannot be “backed up.” Attempting to back up a flat-towed dinghy is likely to cause significant stresses and permanent damage to both the tow hitch and dinghy steering system. The caster angle and steering axis inclination (SAI) built into the dinghy's steering system, which normally stabilizes steering when the dinghy is driven forward as a conventional vehicle, will work to turn the dinghy's front wheels the wrong way when the dinghy is being backed up with the RV. Even the slightest tail swing by the tow vehicle against the front of the dinghy will destabilize the dinghy's steering system and cause the dinghy's wheels to rotate violently against the steering mechanical stops, resulting in severe stresses. Moreover, once the dinghy's front tires are fully turned they are essentially perpendicular to the direction of travel, and continuing to reverse the dinghy will push the tires sideways, causing serious damage to the dinghy.
When the frame of the dinghy is pushed in reverse from the front end by the tow hitch, the caster angle in the steering attempts to swing the front wheels around to face rearward in a manner similar to the front caster wheels on a shopping cart. The slightest lateral force will begin the steering rotation, and rotation will proceed rapidly as the steering angle increases. When the steering system hits the left or right rotational stop, it does so with a heavy impact, even at very low speed, putting severe load on the dinghy's steering system and on the tow hitch and RV frame.
This limitation of being unable to back up a flat-towed dinghy puts the RV driver at a strong disadvantage when entering an unfamiliar area such as a store parking lot or side road. The driver must proceed with extreme caution and try to simultaneously search out an egress route while also studying the entrance route. If the RV driver is unable to exit a location by driving forward, the only option is to stop the RV in a spot that affords the least blockage of traffic, lock the brakes on the RV, disconnect the dinghy, and drive the dinghy to a safe parking area. The driver must then return to the RV and reposition it toward the exit, then return to the dinghy, maneuver it back to the RV, reconnect the tow hitch, and exit. In an area with high traffic, such as a shopping mall or busy street, this procedure becomes a serious and dangerous situation with blocked traffic and impatient drivers trying to dodge the blockage. On a grade, the disconnect and reconnect of the dinghy to the RV can become difficult or even hazardous, and may require two people.
Prior art such as U.S. Pat. No. 5,560,628 by Horn offers one solution to the problem of backing a flat-towed dinghy by lifting the front end of the dinghy completely off the ground, such that the RV carries the dinghy's weight in a manner similar to a tow truck. Horn discloses a lift using a motorized screw and hitch frame that attaches to a hitch and coupling at the front of the towed vehicle, and elevates the frame of the towed vehicle until the front tires clear the ground. Similarly, U.S. Pat. No. 7,318,698 by Gipson teaches a rear-extending linkage and power system to lift the front wheels of the towed vehicle clear of the ground. While these systems achieve their objective, they require extensive modification to the RV frame to withstand the dinghy's front weight, which can be 2000 to 3000 pounds. The lift devices are heavy, complex, and expensive. Also, most dinghies are not constructed for single-point lifting and towing on the frame, and may require extensive modification.
There is also a great deal of prior art, including dollies, carriages, and tire buoys, that carries the weight of a wheel that is still attached to a vehicle, such as the devices taught in U.S. Pat. No. 834,146 by Lewis and U.S. Pat. No. 863,122 by Webber. Other wheel carriers, such as those taught in U.S. Pat. No. 2,226,521 by McNamara and U.S. Pat. No. 3,224,611 by Smuck, are intended to allow a vehicle with a flat tire to be driven to a service location without having to change the flat tire. However, these devices, and related prior art, are not used on modern dinghies attached to RVs because the devices do not address the peculiar loading and forces exerted on a dinghy that is coupled to an RV. Specifically, the prior art wheel carriers are not designed to overcome the steering caster and steering axis inclination (SAI) forces that are created by the lateral forces that occur when a towing vehicle pushes a towed vehicle in reverse from a tow hitch attached to the front of the towed vehicle.
Accordingly, it is an object of the present disclosure to provide a means of backing up an RV with a flat-towed dinghy attached.
It is another object of the present disclosure to provide a means for backing up a flat-towed dinghy in a familiar manner by which the dinghy behaves and steers like a conventional trailer.
It is another object of the present disclosure to provide a flat-towed dinghy backup device that is inexpensive, simple, and easy to carry and store.
It is another object of the present disclosure to provide a flat-towed dinghy backup device that does not require modifications or attachments to either the RV or dinghy.
It is another object of the present disclosure to provide a wheel carrier that disengages the front wheels of a flat-towed dinghy from the road surface while backing up the dinghy.
It is another object of the present disclosure to provide a dinghy backup system that can be easily stowed in either the dinghy or RV.
It is another object of the present disclosure to provide a dinghy backup carrier that passively locks to the road surface as the dinghy backs up onto the carrier and as the dinghy drives off the carrier.
It is another object of the present disclosure to provide a dinghy wheel carrier that overcomes the turning force from the dinghy front wheels' positive caster angle and SAI when the dinghy is being backed up.
It is another object of the present disclosure to provide a dinghy wheel carrier that does not require the dinghy to lock its brakes while the carrier is being used.